The administration of granulocyte colony-stimulating factor (G-CSF) to increase the white blood cell count in granulocyte donors prior to donation is becoming an increasingly common practice. G-CSF is given subcutaneously to the donor on the day prior to donation, generally 12 to 24 hours before the start of apheresis. It would be advantageous to be able to give G-CSF and collect granulocytes on the same day. However, the single most important factor in optimizing granulocyte collection is the donor's pre-collection granulocyte count. The purpose of this study is to assess granulocyte counts in healthy subjects during an 8-hour period after a single 5 mcg/kg intravenous or subcutaneous dose of G-CSF with or without dexamethasone. Sixteen subjects were studied. Each donor was studied four separate times. The four mobilization protocols were G-CSF 5 mcg/kg given intravenously, G-CSF 5 mcg/kg subcutaneously, G-CSF 5 mcg/kg intravenously plus dexamethasone 8 mg orally, and G-CSF 5 mcg/kg subcutaneously plus dexamethasone 8 mg orally. The order of the route of administration was assigned randomly. White blood cell count and granulocyte counts and were measured before G-CSF administration and at 1/2, 1, 2, 4, 6, 8, and 24 hours after administration. The granulocytes counts measured within the first 8 hours after G-CSF were compared with counts measured 24 hours after G-CSF. We found that granulocyte counts 8 hours after the administration of the agenets are similar to the counts after 24 hours, granulocyte mobilization with intravenous and subcutaneous G-CSF was similar, and granulocyte mobilization with G-CSF plus dexamethasone was better that mobilization with G-CSF alone.